Manufacture of strong fibrous material



United States Patent Q 3,345,201 MANUFACTURE OF STRONG FIBROUS MATERIAL Ernest M. Crowell, Beverly, Mass., assignor to United Shoe Machinery Corporation, Boston, Mass., :1 corporation of New Jersey No Drawing. Filed Mar. 31, 1964, Ser. No. 356,022 8 Claims. (Cl. 117-63) meshed fibers as a fiber structure extending through the mass in a relation in whichthe collagen fiber structure resists displacement of the intermeshed fibers. In that process lightly tanned collagen is suspended in an aqueous medium as distinct slightly swollen fibers of microscopicsize and this suspension is caused to penetrate and fill the open spaces in intermeshed fibrous masses particularly non-woven fiber masses. Thereafter, by altering the conditions within the sheet the fibers are deswelled and associated with each other as a larger collagen fiber structure associated with the intermeshed fibers.

It has been found that, particularly where the intermeshed fiber mass or sheet has hydrophilic characteristics the content of collagen fiber in finished sheets may not be as uniform as is desired.

It is an object of the present invention to provide a method for making strong fibrous sheet materials of the type disclosed in which the collagen fiber content is distributed more uniformly.

To this end and in accordance with a feature of the present invention, the inter-meshed textile fiber sheet material .;is-treated .with a binderbefore association with the collagen fiber suspension; and at a later stage the binder is redistributed and in some cases at least partially removed. The treated fiber sheet has the ability to take up uniformly and rapidly a collagen fiber suspension and to retain a high collagen fibercontent and the ultimate sheet has desirable strength, tear resistance and flexibility.

The method of the present invention is of particular advantage in the manufacture of leather-like sheet materials where a collagen fiber suspension is introduced into non-- woven intermeshed fiber sheet materials, although some of the advantages of the method may be obtainable also with the woven fiber sheets. A wide variety of fibers in intermeshed sheet form may be used. Thus, sheets of fibers of nylon, polyacrylic esters (Orlon), polyesters (Dacron), polypropylene, wool, extruded cellulosic fibers such as viscose or cellulose acetate and others are useful. It has also been found possible to use a sheet of collagen fibrous material of greater fiber lengththan the fiber of the relation formed by treating a mat ofeross laid or random,

laid fibers with barbed needles to improve the intermeshing of the fibers. A fiber density and relation which have been found very satisfactory are those in fiber mats having apparent densities ofthe order of from about 1 to about some extent hydrophilic such as nylon fibers, extruded.

3,345,201 Patented Oct. 3, 1967 ICC 5 pounds per cubic .foot. Useful materials include nylon fiber mats weighing 4 oz. per sq. yd. and having a thickness of 0.15" and weighing 6 oz. per sq. yd. and having a thickness of 0.175. Another highly satisfactory material' is a polypropylene fiber mat having a density of 7 oz. per sq. yd. and a thickness of 0.5". It is preferred that the fibers be relatively fine, suitably, within the range of from 0.5-5 denier.

In these mats the fibers are capable ,of movement relative to other fibers.- Particularly withfibers which are to cellulosic fibers such as viscose or cellulose acetate, and wool fibers, the action of the water of the aqueous suspen sion of collagen fibers has a,softening effect which results.

in undesired and irregular compaction of the mats under the forces exerted in impregnating the mats with the collagen fiber suspension.

Openness of the intermeshed fiber sheets for rapid uniform impregnation with collagen fiber slurry may be maintained by treating a sheet with a binder material to. hold the fibers against compaction. But it has been found difiicult to control the amount of binder to provide, on

the one hand, enough binder to resist major displacement of the intermeshed fibers at the time of impregnation and,

on the other hand, to insure that the amount and disposi-' limited movement in the final sheet, the tear strength of the sheet material becomes undesirably low.

, This difi'iculty is'avoided by the present method through a combination of the-treatment of the intermeshed fiber sheets with special soluble binder materials to give resistance to compaction, with the step of redistributing and, in some instances, at least partially removing binder material by the action of treating-liquids at a later stage.

The treating liquid may be the liquid phase of the collagen fiber suspension itself'or may be a solvent. Where the collagen fiber suspension effects the redistribution or partial removal of. the binder material, the binder must be one which is slowly soluble in order that it may be efiective to hold the fibers against compaction during the impregnati-on stepbefore dissolving to an extent to lose its ability to hold the intermeshedfiber sheet open. These soluble binders maybe used in a percentage so great as to give a fiber holding and rigidifying action which would be expected to reduce tearstrength since this undesirable action is reduced or eliminated by the redistribution or removal of excess binder.

In' addition to the strictly mechanical action of keeping Open the interfiber spaces of an intermeshed fiber sheet to aid'impregnation, the binder material may be selected,

fiber slurry, in order to prevent precipitation or coagula-w tion of collagen fiber at the surface of the fiber sheet which might prevent further penetration of the collagen fiber suspension. into the interior of the sheet.

- Binder compositions which have been found suitable include soluble resins and cellulosic plastics and include tate, diflicultly soluble tanning agents and so on. Where these materials are compatible they may be used in admixture with each other. These materials may be applied as solutions or dispersions in liquid vehicles or as fine solid particles. The binders are preferably used in amount to provide from about 10% up to about 100% by weight based on the Weight of the fibers of the intermeshed fiber sheet. After impregnation of the fiber sheet with a solution or dispersion, the sheet is treated to remove the vehi cle, for example by drying of volatile liquids or with a coagulating agent and physical separation of the liquid vehicle to deposit the stabilizing agent or binder in the sheet in a relation holding the intenmeshed fibers against major displacement.

Uniform penetration and association of collagen fibers in thesheet is secured by balancing of the maintained openness of the treated intermeshed fiber sheet and the properties of the collagen fiber dispersion to insure cooperation with the treated sheet. That is, collagen fiber dispersions differ in their ability to penetrate openings in an intermeshed fiber sheet so that, for example with a fiber sheet of a given openness, a highly penetrating suspension will penetrate readily while another suspension may deposit fibers at the surface of the intermeshed fiber sheet to blind" the sheet, ie to block it against further penetration by the suspension. Again a highly penetrating suspension may pass through an intermeshed fiber sheet leaving only a low proportion of collagen fiber within the sheet while a less penetrating suspension may leave a high percentage of collagen fiber within the intermeshed fiber sheet. A further factor is that the blinding of areas of a fiber sheet by deposit of collagen fibers on its surface due to mismatching of the penetrating ability of the collagen fiber suspension and the openness of the sheet is a self-accelerating action since the blinded area impedes passage of the suspension.

Stabilizing the openness of a sheet of intermeshed fibers by a pretreatment of the intermeshed fiber sheet to deposit a binder material reduces the criticality of the relation between penetrating ability of the suspension and the openness of the intermeshed fiber sheet. Collagen fiber suspensions may be used in the present process which have a greater tendency to separate from suspension than is possible for use with unstabilized fiber sheets. Such suspensions give a high efliciency of fiber utilization and a high collagen fiber content in the finished sheet.

The suspension of microscopic lightly tanned collagen fibers used in the present process may be that described in greater detail in the applications of Tu referred to above. Briefly, the suspension is prepared by beating in water the collagen source, for example skin or hide, under condi tions which limit swelling of the collagen to reduce it to fibers of microscopic size suspended in the water in a manner allowing the fibers relatively free movement in the suspension. The condition is markedly different from that referred to as colloidal in which collagen is reduced to a swollen viscous mass. In the preferred suspension, the collagen material will be lightly tanned, for example to an extent comparable to A to preferably not over 3% of combined aldehyde such as formaldehyde or glyoxal based on the dried weight of the skin material, and the resulting suspension will be adjusted to a pH somewhat outside the isoelectric range of the collagen fibers of the suspension. For impregnation, the suspension will comprise distinct, noncolloidal fibers having a length of from about 0.001 mm. to not over about 4 mm. and preferably not over about 1 mm. in length.

Because of the wide variation in properties of collagen source material and the nature of the fibers in suspension resulting from the beating operation, the suspension after adjustment a pH either above or below the isoelectric range is calibrated for cooperation with the fiber sheet to -be used by filtration through a mat of intermeshed fibers With mats of the character employed for making a sheet and using a vacuum of of mercury, the suspension of fibers is adjusted as to pH and concentration of fibers to,

provide a filtration time of from about one-quarter minute to about two minutes for passage of 600 ml. through a 6" diameter circular section of mat. Penetration ability increases as the pH departs from the isoelectric range so that a suspension having inadequate penetration characteristics, for example requiring over about two minutes for penetration into and through a given mat may be brought to a siutably high penetration value by adjusting its pH to a value farther removed from the isoelectric range. Conversely, a suspension having a high penetration ability and inadequate or undesirably low retention within the fiber sheet may be improved as to these latter properties by adjusting the pH to a value closer to the isoelectric range. Also the rate of penetration is greater with lower concentration of fibers in the suspension, and penetration may be improved by diluting the suspension.

After adjustment of the suspension to a pH value giving useful penetration characteristics for the selected intermeshed fiber sheet material, the actual manufacture of leatherlike sheet material is begun involving penetration of the stabilized mat with the collagen fiber suspension. This penetration may be efiected in various ways as by impregnation of the intermeshed fiber sheet with the suspension, using vacuum or pressure for forcing the suspension into a screen supported fiber sheet, or by spreading the suspension on the surface of a fibrous sheet and working it in. In each of these various forms of procedure for penetration, the stabilizing action of the treatment of the fiber sheet before penetration offers advantages both in effective retention of openness for entry of the suspension into the fiber sheet and by maintaining the dimensions of the sheet against change in the course of working or manipulating the sheet.

It is observed particularly with intermeshed fiber sheets stabilized by treatment with diificultly soluble resins carrying a charge opposite to that of the charge on the collagen fiber, e.g. treatment with a reactive aldehyde resin such as an acid'catalyzed resorcinol formaldehyde resin, i.e., Novolac, solution or a difficultly soluble vegetable tanning material and drying, that the suspension penetrates Well and that during and after penetration there is a precipitating action on the collagen fiber of the suspension within the sheet as indicated by development of an opaque character in the sheet. It appears that this is due to the delayed solution of the deposited material. That is, the slow solution of the material allows penetration of the sheet without hindrance; but progressively increasing amounts of material dissolved by the aqueous phase of the suspension apparently act on the collagen fiber in suspension to neutralize its charge and cause it to precipitate.

With regard to the use of mats treated for stabilization by use of nitrocellulose or other resins which are not soluble in the aqueous phase of the suspension, softer sheets capable of greater fiber movement may be obtained by dewatering these sheets using a solvent such as acetone or by solvent treatment of the sheets after they have been dewatered by other means. The solvent extracts or redistributes the resin, e.g., nitrocellulose, so that it no longer interferes with desirable movement of the intermeshed fibers.

The following examples are given to aid in understanding the invention and it is to be understood that the invention is not restricted to the conditions, procedures or materials set forth in the examples.

Example I A solvent mixture comprising 40 parts by weight of water and 225 parts by weight of denatured alcohol was prepared and in this was dissolved 40 parts by weight of an alcohol-soluble nylon (Zytel 61) and 40 parts by Weight of an acid-catalyzed permanently fusible resorcinol formaldehyde resin.

A needle loomed nonwoven nylon fiber mat having a weight of 6 oz. per sq. yd., a thickness of 0.175" and a fiber denier of 3 was dipped in the solution to impregnate it, removed, squeezed to remove excess solution and air dried. The mat picked up about 26% by weight of combined nylon and resorcinol aldehyde resins and was flexible and resilient so that when compressed it rapidly returned to its original thickness.

An aqueous dispersion of collagen fibers of microscopic size was prepared by tanning hide material to a formaldehyde content of about 0.4 and beating the hide material in a paper beater at a pH of about 5. The collagen fibers thus produced had a length of from about 0.2 to about 1 mm. The suspension was diluted to bring the solids content to about 2% and was acidified by addition of phosphoric acid to bring the pH to about 3.0.

A section of the resin-impregnated and dried nylon fiber mat was disposed on a filter bed provided with means for. applying suction. A quantity of the above-prepared fiber suspension was deposited on the fiber mat in a layer of uniform thickness and suction was applied to pull the suspension into the mat. The suspension entered the mat rapidly and uniformly. Precipitation of the collagen fiber from the dispersion was evidenced by development of an opaque appearance of the mat in the course of impregnation.

The resulting sheet material after removal from the filter bed had a collagen fiber content of about 40% based on the total weight of mat fibers, resins and collagen. The sheet was tanned by immersion for 24 hours in a vegetable tanning bath comprising 30% solids comprised of 80% quebracho extract and 20% of the resorcinol formaldehyde resin. The sheet was removed from the tanning liquor and washed in running tap water for eight hours. It was then squeezed free of excess Water and immersed in a standard fat liquor bath, after which it was removed and dried. The dried sheet was similar to a vegetable tanned leather and its physical properties were in the range of leather.

Example 11 A solvent mixture comprising 25 parts by Weight of water and 15 parts by Weight of acetone was prepared, and in this was dissolved 60 parts by weight of an acid-catalyzed permanently fusible resorcinol formaldehyde resin.

A needle loomed nonwoven nylon fiber mat having a weight of 6 oz. per sq. yd, a thickness of 0.1-75'f and a fiber denier of 3' was dipped in the solution to impregnate it, removed, squeezed to remove excess solution and air dried. Themat was found to have picked up about 75% by weight of resorcinol aldehyde resins based on the original weight of the mat and when compressed rapldly returned to its original thickness.

A further portion of the same aqueous dispersion of collagen fibers of microscopic size as used in Example I was diluted to bring the solids content to about 2% and was acidified by addition of phosphoric acid to bring the pH to about 3.0.

A section of the resin-impregnated and dried nylon fiber mat was disposed on a filter bed provided with means for applying suction. A quantity of the above-prepared fiber suspension was deposited on the fiber mat in a layer of uniform thickness and suction was applied to pull the suspension into the mat. The suspension entered the mat rapidly and uniformly. Precipitation of the collagen fiber from the dispersion was evidenced by development of opacity during impregnation. The resulting sheet material after removal from the filter bed had a collagen fiber content of about 30% by weight. The sheet was tanned, washed, fat liquored and dried as in Example I. The dried sheet was similar to to a vegetable tanned leather and its physical properties were in the range of leather.

Example 111 A 4% solution of nitrocellulose in acetone was prepared and a needle loomed nonwoven nylon fiber mat having a weight of 7 oz. per sq. yd., a thickness of 0.175" and a fiber denier of 3 was dipped in the solution to impregnate it. The mat was removed from the solution, squeezed to remove excess and allowed to air dry. The mat picked up about 18.5% of nitrocellulose based on the weight of the mat fiber and was flexible and resilient.

An aqueous dispersion of collagen fibers of microscopic size similar to that used in Example I, but having a solids content of about 3%, was acidified by addition of phosphoric acid to bring the pH toabout 2.84. A section of the nitrocellulose impregnated and dried fiber mat was disposed on a filter bed provided with means for applying suction. A quantity of the above fiber suspension was deposited on the fiber mat in a layer of uniform thickness and suction was applied to pull the suspension into the mat. The suspension entered the mat rapidly and uniformly; but there was no indication of precipitation of the collagen fiber. The resulting sheet after removal from the filter bed showed a collagen fiber pick up of about 32%. While still wet with water, the sheet was placed in a chrome tanning bath containing 1% by weight chromium calculated as Cr 0 and 2% by weight of sodium formate. After standing overnight in this tanning bath the sheet was removed, immersed in warm tap water for 6 hours, pressed between filter papers to remove further Water and disposed in a fat liquor bath. After fat liquoring' the sheet was removed and dried. Thereafter, the sheet was dipped momentarily in acetone and hung to dry. The sheet which was somewhat stiff prior to the acetone treatment had improved flexibility and softness when dried after the acetone treatment indicating a redistribution of the nitrocellulose content of the sheet. 7

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is: p

1. In a process of forming a strong fibrous material including the steps of penetrating the thickness of a mat of nonwoven intermeshed fibers with an aqueous suspension of swollen distinct fine collagen fibers of microscopic size and removing the swelling water from said collagen to reaggregate the fibers into a larger collagen fiber structure reinforcing said intermeshed fibers against displacement, the improvement which comprises depositing a soluble binder insaid mat of fibers before penetration by the collagen fiber suspension, said binder being at most slowly soluble in the aqueous suspension and being deposited in amount of from 10% to by weight based 'on the Weight of the fibers of the mat'to cooperate with said fibers in resisting compaction of said mat during penetration with said collagen fiber suspension, and "at least partially dissolving said binder and redistributing it in said "mat-ata stage in said process when collagen fibers have penetrated said mat.

2. In a process of forming a strong'fibrous material including the steps of penetrating the thickness of a mat of nonwoven intermeshed fibers with an aqueous suspension of swollen distinct fine collagen fibers of microscopic size and removing the swelling water from said collagen to reaggregate the fibers into a larger collagen fiber structure reinforcing said intermeshed fibers against displacement, the improvement which comprises depositing a binder in said mat of fibers before penetration by the collagen fiber suspension, said binder being deposited in amount of from about 10% to about 100% by weight based on the weight of the fibers of the mat and resisting compaction of said mat during penetration with said collagen fiber suspension, said deposited binder being slowly soluble in the water component of said collagen fiber suspension, and at least partially dissolving said binder and redistributing it in said mat by the water component of collagen fiber suspension penetrating said mat.

3. In a process of forming a leather-like material including the steps of penetrating the thickness of a mat of nonwoven intermeshed fibers with an aqueous suspension of swollen distinct fine collagen fibers of microscopic size and removing the swelling water from said collagen to reaggregate the fibers into a larger collagen fiber structure reinforcing said intermeshed fibers against displace ment, the improvement which comprises depositing a binder in said mat of fibers before penetration by the collagen fiber suspension, said binder being deposited in amount of from about 10% to about 100% by weight based on the weight of the fibers of the mat and resisting compaction of said mat during penetration with said collagen fiber suspension, said deposited binder being slowly soluble in the Water component of said collagen fiber suspension, and at least partially dissolving said nonwoven intermeshed fibers with an aqueous suspension of swollen distinct fine collagen fibers of microscopic size and removing the swelling water from said collagen to reaggregate the fibers into a larger collagen fiber structure reinforcing said intermeshed fibers against displacement, the improvement which comprises depositing permanently fusible acid-catalyzed resorcinol resin in said mat of fibers before penetration by the collagen fiber suspension, said resin being deposited in amount of from about 10% to about 100% by weight based on the weight of the fibers of the mat and resisting compaction of said mat during penetration with said collagen fiber suspension, said deposited resin being slowly soluble in the water component of said collagen fiber suspension, and at least partially dissolving said resin and redistributing it in said mat by the water component of collagen fiber suspension penetrating said mat, said resin being active in solution at least partially to deswell said collagen fibers causing them to deposit within said mat at an accelerated rate over the rate of deposition in a mat without such resin.

6. The process as defined in claim in which a slowly soluble vegetable tanning agent is deposited on said fibers before penetration of the mat by collagen fiber suspension.

7. In a process of forming a leather-like material including the steps of penetrating the thickness of a mat of nonwoven intermeshed fibers with an aqueous suspension of swollen distinct fine collagen fibers of microscopic size and removing the swelling water from said collagen to reaggregate the fibers into a larger collagen fiber struc* ture reinforcing said intermeshed fibers against displacement, the improvement which comprises depositing resin in said mat of fibers before penetration by the collagen fiber suspension, said resin being deposited in amount of from about 10% to about by weight based on the weight of the fibers of the mat and resisting compaction of said mat during penetration with said collagen fiber suspension, said resinous material being insoluble in the Water component of said aqueous suspension but soluble in a solvent, and treating the mat after impregnation with a solvent for said resin to redistribute said resin in said mat.

8. In a process of forming a leather-like material including the steps of penetrating the thickness of a mat of nonwoven intermeshed fibers with an aqueous suspension of swollen distinct fine collagen fibers of microscopic size and removing the swelling water from said collagen to reaggregate the fibers into a larger collagen fiber structure reinforcing said intermeshed fibers against displacement, the improvement which comprises depositing nitro cellulose in the mat of fibers before penetration by the collagen fiber suspension, said nitrocellulose being deposited in amount of from about 10% to about 100% by weight based on the weight of the fibers of the mat and resisting compaction of said mat during penetration with said collagen fiber suspension and treating the mat after impregnation with a solvent for said nitrocellulose to re distribute it in the mat.

References Cited UNITED STATES PATENTS 1,833,029 11/1931 MacKay.

1,990,121 2/1935 Halloran 117-140 2,040,511 5/1936 Bleyenheuft 117-140 X 2,229,061 l/ 1941 Eustis.

2,339,562 1/1944 Eustis 117 X 2,405,978 8/1946 Pickles et al 117-140 X 2,838,363 6/1958 Veis et a1.

2,934,446 4/1960 Highberger et al. 162-151 X 2,934,447 4/1960 Highberger et a1. 162-151 X 2,973,284 2/1961 Semegen 117138.8 X 3,013,936 12/1961 Iyengar 117 138.8 X 3,034,927 5/1962 Fairclough et al 117-140 3,071,483 1/1963 Tu 106155 3,223,551 12/1965 Tu 117-140 WILLIAM D. MARTIN, Primary Examiner.

T. G. DAVIS, Assistant Examiner. 

1. A PROCESS OF FORMING A STRONG FIBROUS MATERIAL INCLUDING THE STEPS OF PENETRATING THE THICKNESS OF A MAT OF NONWOVEN INTERMESHED FIBERS WITH AN AQUEOUS SUPENSION OF SWOLLEN DISTINCT FINE COLLAGEN FIBERS OF MICROSCOPIC SIZE AND REMOVING THE SWELLING WATER FROM SAID COLLAGEN TO REAGGREGATE THE FIBERS INTO A LARGER COLLAGEN FIBER STRUCTURE REINFORCING SAID INTERMESHED FIBERS AGAINST DISPLACEMENT, THE IMPROVEMENT WHICH COMPRISES DEPOSITING A SOLUBLE THINNER IN SAID MAT OF FIBERS BEFORE PENETRATION BY THE COLLAGEN FIBER SUSPENSION, SAID BINDER BEING AT MOST SLOWLY SOLUBLE IN THE AQUEOUS SUSPENSION AND BEING DEPOSITED IN AMOUNT OF FROM 10% TO 100% BY WEIGHT BASED ON THE WEIGHT OF THE FIBERS OF THE MAT TO COOPERATE WITH SAID FIBERS IN RESISTING COMPACTION OF SAID MAT DURING PENETRATION WITH SAID COLLAGEN FIBER SUSPENSION, AND AT LEAST PARTIALLY DISSOLVING SAID BINDER AND REDISTRIBUTING IT IN SAID MAT AT A STAGE IN SAID PROCESS WHEN COLLAGEN FIBERS HAVE PENETRATED SAID MAT. 